怎么设置左右选择框的右选框的选项全部默认选中

<select multiple="multiple" id="rightSel" style="width:200px;">
			<option>1</option>
			<option>1</option>
			<option>1</option>
			<option>1</option>
</select>

$("#rightSel").find("option").attr("selected",true);